Add manual AI analysis trigger for existing feedback

Implement dashboard functionality to manually trigger AI analysis for
feedback that was submitted before Phase 4 or failed analysis. Adds
detection mechanism to identify which feedback has been analyzed.

Features:
- Manual analysis trigger route: POST /feedback/{id}/analyze
- Detection of whether feedback has been analyzed (analysis.md exists)
- Dashboard UI button showing "Analyze" or "Re-analyze"
- Visual feedback for feedback without text content
- Comprehensive error handling and flash messages

Implementation:
- app/routes/dashboard.py: Added trigger_analysis() route handler
- app/routes/dashboard.py: Updated detail() to pass analysis status
- app/services/feedback_storage.py: Added has_analysis() helper method
- app/templates/dashboard/detail.html: Added analyze button UI
- tests/contract/test_dashboard_routes.py: Added 3 new contract tests

Testing:
- test_post_trigger_analysis_success: Successful manual analysis
- test_post_trigger_analysis_no_content: Reject empty content
- test_post_trigger_analysis_unauthenticated: Auth required
- All 49 tests passing (1 skipped)

User Experience:
- Green box with "Analyze" button for unanalyzed feedback
- Blue box with "Re-analyze" button for already analyzed feedback
- Red box with info message for feedback without text content
- Flash messages show success/error after analysis

🤖 Generated with [Claude Code](https://claude.com/claude-code)

Co-Authored-By: Claude <noreply@anthropic.com>

app/services/feedback_storage.py

@@ -529,3 +529,20 @@ class FeedbackStorageService:
         """
         # Use the raw analysis from Claude, which is already formatted
         return analysis_result.raw_analysis
+
+    @staticmethod
+    def has_analysis(product_id, feedback_id):
+        """Check if feedback has been analyzed
+
+        Args:
+            product_id: Product ID
+            feedback_id: Feedback ID
+
+        Returns:
+            bool: True if analysis.md exists, False otherwise
+        """
+        data_dir = current_app.config['DATA_DIR']
+        analysis_file = os.path.join(
+            data_dir, 'products', product_id, 'feedback', feedback_id, 'analysis.md'
+        )
+        return os.path.exists(analysis_file)